Arguments

rows, cols

A set of variables or expressions quoted by
vars() and defining faceting groups on the rows or columns
dimension. The variables can be named (the names are passed to
labeller).

For compatibility with the classic interface, rows can also be
a formula with the rows (of the tabular display) on the LHS and
the columns (of the tabular display) on the RHS; the dot in the
formula is used to indicate there should be no faceting on this
dimension (either row or column).

scales

Are scales shared across all facets (the default,
"fixed"), or do they vary across rows ("free_x"),
columns ("free_y"), or both rows and columns ("free")?

space

If "fixed", the default, all panels have the same size.
If "free_y" their height will be proportional to the length of the
y scale; if "free_x" their width will be proportional to the
length of the x scale; or if "free" both height and width will
vary. This setting has no effect unless the appropriate scales also vary.

shrink

If TRUE, will shrink scales to fit output of
statistics, not raw data. If FALSE, will be range of raw data
before statistical summary.

labeller

A function that takes one data frame of labels and
returns a list or data frame of character vectors. Each input
column corresponds to one factor. Thus there will be more than
one with formulae of the type ~cyl + am. Each output
column gets displayed as one separate line in the strip
label. This function should inherit from the "labeller" S3 class
for compatibility with labeller(). See
label_value() for more details and pointers to other
options.

as.table

If TRUE, the default, the facets are laid out like
a table with highest values at the bottom-right. If FALSE, the
facets are laid out like a plot with the highest value at the top-right.

switch

By default, the labels are displayed on the top and
right of the plot. If "x", the top labels will be
displayed to the bottom. If "y", the right-hand side
labels will be displayed to the left. Can also be set to
"both".

drop

If TRUE, the default, all factor levels not used in the
data will automatically be dropped. If FALSE, all factor levels
will be shown, regardless of whether or not they appear in the data.

margins

Either a logical value or a character
vector. Margins are additional facets which contain all the data
for each of the possible values of the faceting variables. If
FALSE, no additional facets are included (the
default). If TRUE, margins are included for all faceting
variables. If specified as a character vector, it is the names of
variables for which margins are to be created.

# To change plot order of facet grid,# change the order of variable levels with factor()# If you combine a facetted dataset with a dataset that lacks those# faceting variables, the data will be repeated across the missing# combinations:df<-data.frame(displ=mean(mpg$displ), cty=mean(mpg$cty))
p +
facet_grid(cols=vars(cyl)) +
geom_point(data=df, colour="red", size=2)

# Free scales -------------------------------------------------------# You can also choose whether the scales should be constant# across all panels (the default), or whether they should be allowed# to varymt<-ggplot(mtcars, aes(mpg, wt, colour=factor(cyl))) +
geom_point()
mt + facet_grid(. ~ cyl, scales="free")

# If scales and space are free, then the mapping between position# and values in the data will be the same across all panels. This# is particularly useful for categorical axesggplot(mpg, aes(drv, model)) +
geom_point() +
facet_grid(manufacturer ~ ., scales="free", space="free") +
theme(strip.text.y=element_text(angle=0))